Engine fan engages and stays on with A/C turned on

[JimmyDw8xb]

I have had this shop do a couple of small things and they have been acceptable to me. They come with a decent reputation locally.
I just try to read forums and learn as much as I can. I am capable of doing almost all of my mechanical needs as far as the truck is concerned. What I don`t know, there is always the internet and you tube videos on almost every thing I would want to know.

BUT, there are some things my 75 year old butt doesn`t want to do. One of my front brake shoes had a crack. So I took it in for front brakes and drums. Mechanic called me, said my right rear wheel had a leaky wheel seal. I stopped down at the shop and chatted him up. I`ll admit to being a bit anal, so figuring this truck had only ran spring and fall 40,000 miles over 9 years are all the grain farmer put on it and said they serviced it once a year. So to make a long story short, I told him to just replace all the wheel seals figuring that if one went bad, how far behind were the others. so that led to having them do the annual DOT inspection, and by the way.....check the air conditioner..He asked if it had been working and I said no. He said, "I`ll evacuate it and charge it"

So that`s how I got to here.. He had just charged it within the previous 24 hours and I`m thinking that it sure leaked off the new freon really quickly. I`m assuming he did what he said he was going to do. I don`t know much about hvac but I thought you had to vacuum out the system, then refill into the vacuum with fresh freon. I know that`s over simplified {if right at all} But if the system has a leak, you could not get or keep a vacuum and that tells you if there is a leak? could the work push some seal or something out of kilter, or provoke a near failure into going bad?